But be prepared for that same child to be more aggressive toward you and his siblings, his friends and his eventual spouse. Oh, and get ready for some other antisocial behaviors too.

A new analysis of two decades of research on the long-term effects of physical punishment in children concludes that spanking doesn’t work and can actually wreak havoc on kids’ long-term development, according to an article published Monday in the Canadian Medical Association Journal.

Studying physical punishment is difficult for researchers, who can’t randomly assign children to groups that are hit and those that aren’t. Instead, they follow children over many years, monitor how much they’re spanked, and then take measure of their aggression over time. “We find children who are physically punished get more aggressive over time and those who are not physically punished get less aggressive over time,” says Joan Durrant, the article’s lead author and a child clinical psychologist and professor of family social sciences at the University of Manitoba.

In fact, regardless of the age of the children or the size of the sample, none of more than 80 studies on the effects of physical punishment have succeeded in finding positive associations. “If someone were to hit us to change our behavior, it might harm our relationship with that person. We might feel resentful,” says Durrant. “It’s no different for children. It’s not a constructive thing to do.”

Children who are spanked may feel depressed and devalued, and their sense of self-worth can suffer. Harsh punishments can wind up backfiring because they can foster lying in children who are desperate to avoid being spanked. Later in life, physical punishment is linked to mental-health problems including depression, anxiety and drug and alcohol use. There’s neuroimaging evidence that physical punishment may alter parts of the brain involved in performance on IQ tests and up the likelihood of substance abuse. And there’s also early data that spanking could affect areas of the brain involved in emotion and stress regulation.

Yet, as I wrote last summer in a story about the first real-time study of parents spanking their children, some research has found that up to 90% of parents say they use corporal punishment:

Despite a battery of disciplinary techniques, including the infamous “time out,” redirection and the increasing emphasis on positive discipline (try substituting “hold the cup carefully” for “don’t spill your juice”), spanking and slapping are still pretty popular.

Moms and dads who spank do so because they believe it’s effective, and research actually shows that it is — in the short term. A child reaching for a tempting object will stop if he gets swatted. “It does work in the immediate moment, but beyond that, in most cases, it’s very ineffective,” says George Holden, the study’s author and a professor of psychology at Southern Methodist University. “The most common long-term consequence is that children learn to use aggression.”

Case in point: one mother in the study hit her toddler after the toddler either hit or kicked the mother, admonishing, “This is to help you remember not to hit your mother.”

“The irony is just amazing,” says Holden.

In some countries, spanking is not a choice. Durrant is currently living in Sweden, where she’s researching child-and-family policies and the evolution of that country’s law prohibiting physical discipline of children. In 1979, Sweden was the first country to pass such legislation; now 32 countries — including much of Europe, Costa Rica, Israel, Tunisia and Kenya — have a similar law.

Neither the U.S. nor Canada has gotten on board. “Whenever I mention the law, there is an assumption that this is government telling me how to raise my child,” says Durrant. “[But in Sweden] they see it as a way to make sure children get the best start possible in life.”

Parents who spank often do so by default. Many, particularly those who were hit themselves, find that spanking is the only disciplinary tactic in their toolbox. Doctors are in a position to change that by educating parents about the stages of normal child development, recommending alternative ways to discipline and referring interested parents to appropriate resources and parenting classes. In Sweden, for example, new parents are hooked up with support groups and given information about developmental stages.

As a result, parents understand their children aren’t being intentional obstructionists; it’s just par for the course. “When children see someone resolve conflict with aggression, they are more likely to learn that behavior,” says Durrant. “Two-year-olds are the most aggressive people in the world. They don’t understand the impact of their behavior, and they can’t inhibit themselves. So the more a child sees someone resolving conflict with aggression, the more aggressive they become.”

A young toddler who upends her cereal bowl on her head probably isn’t being ornery; she’s just curious to see what will happen. Durrant likes to use her son as an example. When he was 3, he dropped his dad’s toothbrush into the toilet. Another parent might have yelled, but Durrant’s academic background helped her realize that he was just experimenting: he dropped objects into water floating in sinks and bathtubs with nary a scolding; why not toilets too? “I explained what goes into toilets and then said, Do you think Daddy is going to want to put that toothbrush in his mouth now?” Message transmitted with no yelling.

P.S. Durrant’s son never dropped anything verboten into the toilet again.